1. Field of the Invention
This invention relates to a semiconductor device and a method for manufacturing the same, and more particularly to a semiconductor device including both lateral and vertical MOSFET and a method for manufacturing the same.
2. Background Art
In a DC-DC converter, typically, a high-side transistor and a low-side transistor are connected in series between an input potential and a ground potential, and a smoothing circuit composed of an inductor and a capacitor is connected between the junction of these transistors and an output terminal. A control circuit applies a prescribed control signal to the gate electrode of these transistors to produce a given potential at the output terminal.
Recently, there is a demand for downsizing the DC-DC converter to improve the voltage conversion efficiency. For example, JP-A-2005-294464 (Kokai) discloses a technique for housing in one package a semiconductor chip including a high-side transistor, a semiconductor chip including a low-side transistor, and a semiconductor chip including a control circuit. However, in this technique, a plurality of semiconductor chips need to be connected to each other by bonding wires. Thus, there is a limit to the downsizing and efficiency improvement of the DC-DC converter.
To further downsize the DC-DC converter, it may be contemplated to form a high-side transistor and a low-side transistor on the same chip. However, unfortunately, this complicates interconnection and increases interconnect resistance, which contrarily decreases the voltage conversion efficiency (see, e.g., JP-A-9-213956 (Kokai) (1997)).